1. Field of the Invention
This invention relates to a crystalline polyolefinpolylactone graft copolymer which is effective as a compatibilizing agent or as a modifier for engineering thermoplastic compositions. In particular, the graft copolymer is an effective modifier for engineering thermoplastic compositions comprising thermoplastic polymers that are at least partially miscible with the selected polylactone and will be suitable as a compatibilizing agent for such engineering thermoplastics also additionally comprising a crystalline polyolefin, such as polypropylene or polyethylene.
2. Background Information
Many engineering resins, such as polycarbonate, styreneacrylo-nitrile, and polystyrene/polyphenylene oxide, possess outstanding mechanical properties such as impact resistance, heat resistance, rigidity and dimensional stability. However, such resins suffer from problems with low temperature impact strength, brittleness, resistance to hydrocarbon solvents and difficulties in mold processing. Polypropylene is another well-known engineering thermoplastic. It is one of the lightest major plastics yet because of its high crystallinity, is known to possess high tensile strength, stiffness and hardness. These characteristics allow finished materials made thereof, having good gloss and high resistance to marring. Further, its high melting point allows it to be subjected to elevated temperatures without loss of high tensile strength. High density polyethylene similarly is a relatively low-cost material that because of its high crystallinity exhibits high tensile strength and impact strength. Also it is hydrophobic and can reduce moisture absorption in engineering plastic resins. For both polypropylene and high density polyethylene, their relatively inexpensive availability makes them highly desirable as a component for engineering plastic resins.
It is also well-known that two or more polymers may be blended together to form a wide variety of random or structured morphologies to obtain products that potentially offer desirable combinations of characteristics. However, it may difficult or impossible in practice to achieve many potential combinations through simple blending because of some inherent fundamental problems. Frequently, the two polymers are thermodynamically immiscible which precludes generating a truly homogeneous product. This may not be a problem per se, since often it is desirable to have a two-phase structure. However, typically, high interfacial tension will occur and poor adhesion results between the two phases. This interfacial tension contributes, along with high viscosities, to inherent difficulties in achieving desired degrees of dispersion for random mixtures, and to their subsequent lack of stability. Phase separation or stratification during later processing or use can thus often result. Poor adhesion leads in part, to very weak and brittle mechanical behavior often observed in dispersed blends and may render some highly desired morphologies impossible.
It is generally known that the presence of certain polymeric species, usually block or graft polymers, suitably chosen, may serve as effective compatibilizers. A compatibilizer in this sense is a polymer that has the characteristics of properties permitting it to stabilize, or compatibilize, a multi-phase polymer blend. Compatibilization is believed to occur because of the preferential location of the compatibilizing agent at the interface of the phases in a blend. This preferential location is believed to occur as a result of entanglement of respective segments of the compatibilizer in the phases to which the phases are similar in chemical characteristics. This increases the adhesion between the phases and, as a result of reduced surface energy between the phases, better dispersion is permitted.
U.S. Pat. No. 4,140,482 discloses the formation of a graft copolymer of nylon and polyethylene as part of a blend of nylon and polyethylene. The presence of the graft copolymer is said to have a dramatic effect on the properties of the blends (in this case its permeability) which can be related to its function as compatibilizer. Likewise, U.S. Pat. No. 4,264,747 discloses compatibilizing a blend of styrene acrylo-nitrile resins with styrene-ethylene-butylene-styrene block copolymer where the copolymer has been made compatible with the styrene acrylo-nitrile resin by forming a graft copolymer compatibilizer by grafting a polar monomer which may be the styrene acrylo-nitrile resin onto the block copolymer backbone.
There is, specifically, a continuing need for an improved modifier and/or compatibilizing agent for engineering thermoplastic compositions, such as polycarbonates, with crystalline polyolefins. Continuing work in this area is exemplified in Japanese Patent Application 63-258883 wherein a proposed graft copolymer of a polyester and a polyolefin is suggested for the use as a solubilizer in a resin of a polycarbonate and polyolefin. The modified polyolefin precursor with a graft copolymer is said to contain 0.2-5.0 mol % of epoxy groups that are reactive with a terminal carboxyl group on the selected polyester component of the graft copolymer.
Certain graft polymers containing polylactones are known. EP-A-0181587 relates to anti-static or electrically semiconductive thermoplastic polymer blends in which a first polymer containing a electrically conductive substance forms a continuous phase, and a second polymer, of higher melt viscosity than the first, is blended in this first polymer. Included in suggested polymer blends are those where the first polymer may be polycaprolactone and the second polymer may be a maleic-acid-anhydride-modified polyethylene, maleic-acid-anhydride-modified-ethylene-propylene-diene terpolymer, or maleic-acid anhydride-modified polystyrene. It is taught that copolymers may form at the interface between the two polymer phases by mechanism of a chemical reaction. Such reactions can be, for example, catalyzed or uncatalyzed esterification, where p-toluenesulfonic acid may be the catalytic agent.
In view of the observed need for novel and improved engineering resin compositions, it is the object of this invention to provide a graft copolymer of crystalline polyolefins and polylactone that is useful in the field of engineering thermoplastic compositions. More specifically, an object of the invention is to provide a crystalline polyolefin based graft copolymer effective as a compatibilization agent for engineering thermoplastic resins comprising as one component, crystalline polyolefin. A method for preparation of this graft copolymer is also a specific objective of this invention.